Assessing the Role of Amygdala Calcitonin Gene-related Peptide Receptors on Chronic Bladder Pain

Background & Aims

Visceral pain is a major health issue that disproportionally affects millions of women worldwide. The mechanisms that control and modulate visceral pain (e.g., bladder pain) are poorly understood. Previous work in our lab shows that the neuropeptide, calcitonin gene-related peptide (CGRP), has divergent functions in the left and right central amygdala (CeA) in a mouse model of bladder pain. The CeA in the right hemisphere of the brain has been shown to increase pain, while the CeA in the left hemisphere has been shown to reduce bladder pain. In this study, we seek to assess the role of CGRP receptors (Calcrl) on the hemispherical and temporal changes of the CeA as bladder pain transitions from acute to chronic/persistent pain.

Methods

For this study, we used a mouse model of bladder pain (100 mg/kg cyclophosphamide, 3 days) to conduct physiology, histology, behavior, and in vivo calcium imaging experiments 2-21 days post-injury (DPI). In the first part of the study, urinary bladder distension and visceromotor responses (UBD-VMR) and bladder histology (hematoxylin and eosin staining) were used to measure bladder pathology progression. In the second study, we administered a CGRP receptor (CGRP-R) antagonist – CGRP8-37 (or vehicle) into the right or left CeA (1 uL of 100 uM) before abdominal von Frey (mechanical sensitivity). In the third study, GRIN lenses were implanted into the CeA of Calcrl-Cre animals to measure the neural activity (via in vivo calcium imaging) of CGRP-R positive cells in the left or right CeA 2-21 DPI.

Results

We found that while cyclophosphamide-induced bladder pain-like behavior in UBD-VMR over time, bladder histology was similar across groups. In the pharmacology study, CGRP8-37 significantly attenuated the development of bladder-like pain when administered in the right CeA, but not the left. Preliminary data in the calcium imaging study indicate that spontaneous neural activity of CGRP-R cells was similar in both hemispheres across time. However, when a stimulus was applied to the pelvic region of the animal (stimulus-evoked) neural activity of CGRP-R cells was increased in the right CeA, compared to the left.

Conclusions

Collectively, these data support the study of cell-specific manipulation of the right CeA to produce bladder pain relief. Furthermore, studying hemispherical differences in pain control will lead to the development and advancement of effective therapies for visceral pain.

References

Allen, H., Chaudhry, S., Hong, V., Lewter, L., Sinha, G., Carrasquillo, Y., Taylor, B., Kolber, B. A parabrachial to amygdala circuit that determines hemispheric lateralization of somatosensory processing. Biol Psychiatry. 2023 Feb 15; 93(4):370-381. PMID:36473754.

Presenting Author